Why would anyone want the job of president? The answers are as different as the men themselves.

For months (and months and months), presidential candidates have subjected themselves to relentless stumping, repetitive fundraising and vicious public scrutiny. They've endured far too many fact-checks, eaten far too many swing-state delicacies, kissed far too many swing-state infants. They've made promises no one could keep and gaffes no one could believe. Even with the exit polls now in sight, it's enough to make any sane person pause and wonder: Why would anyone run for president?

On the record, at least, our candidates cite similar reasons: that this is the most important election in the past however many years — and that they, however unworthy, have the right ideas to make a difference.

But what about the real reasons someone might decide to run? To find that kind of honesty, we must dig deep into the archives, where presidents have addressed the question either privately or long after the fact.

Presidents run because they care about their legacies. John Quincy Adams, who had already served several presidents as ambassador or secretary of State, ran in an age when most candidates politely refused to campaign. Even in his private diary, which would eventually fill more than 50 volumes, he neglected to mention his motivation — except for one entry on May 8, 1824, just as the campaign was heating up.

Whether I ought to wish for success is among the greatest uncertainties of the election. Were it possible to look with philosophical indifference to the event, that is the temper of mind to which I should aspire.... [But] to suffer without feeling is not in human nature; and when I consider that to me alone, of all the candidates before the nation, failure of success would be equivalent to a vote of censure by the nation upon my past service, I cannot dissemble to myself that I have more at stake upon the result than any other individual in the Union.

Presidents run because they obsess over a particular issue. As the election of 1860 approached, Abraham Lincoln and his allies used letters to strategize and predict outcomes in various states. ("You know how it is in Ohio," he sighed to one correspondent.) But while Lincoln never explicitly said why he decided to run, we can infer at least one reason from the letters he wrote after losing the 1858 Senate election to his famous debating partner, Stephen Douglas.

The fight must go on. The cause of civil liberty must not be surrendered at the end of one, or even, one hundred defeats. Douglas had the ingenuity to be supported in the late contest both as the best means to break down, and to uphold the Slave interest. No ingenuity can keep those antagonistic elements in harmony long.... I am glad I made the late race. It gave me a hearing on the great and durable question of the age … [and] I believe I have made some marks which will tell for the cause of civil liberty long after I am gone.

Presidents run because they want power. Political watchers love to speculate on a candidate's motives, something John F. Kennedy knew better than most. Did he end up in politics to please his father, or to measure up to his dead brother? For Kennedy, the answer was simpler, as he revealed at a D.C. dinner party shortly after announcing his run in 1960. The comments were recorded not by a clandestine iPhone-wielding snoop but by a friendly reporter working on a book.

Well, look now, if [I] went to law school … and then I go and become a member of a big firm, and I'm dealing with some dead, deceased man's estate, or I'm perhaps fighting in a divorce case … or let's say more serious work, when you're participating in a case against the DuPont Company in a general antitrust case, which takes two or three years, can you tell me that that compares in interest with being a member of Congress in trying to write a labor bill, or trying to make a speech on foreign policy? I just think that there's no comparison.... Most important is the fact that the president today is the seat of all power.